There are games in which a player operates a player character to defeat an enemy character in a virtual game space using a virtual gun or a sword. For example, when an enemy character appears, the player moves the player character to that position, or aims at that position to defeat the enemy character. Moreover, when the player character is found by an enemy character, the game does not advance in some cases if the player does not defeat that enemy character. In most games, when the player defeats an enemy character, another enemy character newly appears, so that the player cannot complete the game if the player does not defeat enemy characters appearing in sequence. Game devices appropriately allow a new enemy character to appear in accordance with the position, level, etc. of the player character to make the development of the game more amusing, thereby attracting the player's interest.
For example, [Patent Literature 1] discloses a game system that controls the number of enemy characters, the strength thereof, etc. based on the number of players participating in a game or the level of the player character, thereby making the game more amusing without largely deteriorating the game's balance.
Moreover, [Patent Literature 2] discloses a game device that refers to a player's character activity history, and changes the rate of recurrence of enemy characters depending on a position. For example, if a period after the player character starts standing by at a predetermined hole up to a present time is long, the appearance probability of an enemy character at that hole is decreased.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. 2004-160059    Patent Literature 2: Unexamined Japanese Patent Application KOKAI Publication No. H11-53570